You really don’t understand this.
You’re looking at it from a modern POV.
Traditional lactation patterns are NOTHING like today’s. Babies were worn in slings. They nursed a lot — whenever they wanted. The breast was right there and always available.
We speak of babies nursing every two hours and think it’s a lot. A traditional pattern was more like nursing for 15 seconds, then eight minutes later nursing for two minutes. Then half an hour later, nursing for ten minutes. Then for 10 seconds. No schedule was followed. We think of breastfeeding only as getting milk into a baby. But that’s not all it was, traditionally. It kept babies quiet and happy and hydrated. It suppressed menses (it takes a LOT more frequent milk extraction than almost any modern women practice to suppress fertility for several years). We think crying is normal, but to a traditional woman, only an ill child cried.
You cannot apply what you know about modern breastfeeding and childcare to a traditional society.
Another thing … clearly you haven’t nursed if you think you can just leave a nursing baby for an afternoon! The breast is producing milk constantly. Go from nursing frequently to not nursing for a few hours? Ouch! Engorgement like that can lead to mastitis — an extremely bad thing if you have no antibiotics. You’d want to avoid risking that. A woman could hand-express for comfort, but she’d be loathe to do so. Every calorie was needed.
And if you actually did leave your baby for a while, your fertility would return far too soon.
A modern example: I nursed full-term and exclusively. My period came back right away with my daughter because I didn’t pump when we were separated by my PT job. I was able to pump enough milk each morning to sustain her while I worked. But without that constant milk extraction, my fertility came back around 8 weeks after giving birth. Presumably, I’d have conceived soon thereafter if I hadn’t used contraception. With my son, I was home and we weren’t separated at all. My period returned when he was around 18 months old. This seems like a long time for the modern age, but it was far earlier than in a traditional society. You do NOT want to conceive when your child is only 18 months old. You want your babies spaced because you have shit to do. You have to gather. You have to make garments. You have to prepare food. Watch children. Teach skills. Make baskets or other containers … it was a lot, and you couldn’t easily care for more than one young child. Our ancient ancestors nursed SEVEN YEARS. The crunchiest American mom might nurse 3-4 years. There is just no comparison.